At the heart of visual processing that leads to perception is the synthesis of simple features into a coherent whole. Much of that synthesis is the function of the visual cortical areas outside of the primary and secondary visual areas (V1 and V2), in which the component parts of a visual scene, analyzed at earlier stages, are reassembled. A prevailing model has this system operating as a chain of cortical areas, each providing the next with the relevant information. Viewed in anatomical terms, this model accents the rich interconnections among visual areas and sets up a hierarchy through which, as examples, elemental features of form and motion are donated to higher areas by way of their inputs from lower areas. There are many compelling reasons to find this model attractive but limited in one respect, namely the contribution of the pulvinar complex to visual processing. The studies outlined in this proposal address, then, the possibility of a different model, one in which information relayed through the pulvinar plays a vital, enabling role in the late stages of analysis and early stages of synthesis that underlie visual perception. As a complex of many subnuclei, the pulvinar is a much-expanded part of the dorsal thalamus in primates, one that makes up almost half that region in the human brain. In that respect its enlargement across Orders of mammals mirrors precisely the enlargement of non-primary areas of sensory cortex. It is a complex in primates with rich inputs and dense outputs to all areas of extrastriate visual cortex. With these details in mind, specific predictions are outlined in this proposal that will be tested with qualitative and anatomical methods, using both light and electron microscopes. Particular attention will be paid to subnuclei in the pulvinar where synaptic inputs from one area of visual cortex (e.g. V2) innervate neurons that send axons to another area (e.g. V4), since published and preliminary studies strongly suggest that both the corticothalamic and the thalamocortical parts of this loop can be considered as dominant driving inputs. The studies will focus on the pulvinar of a non-human primate species, both as a practical matter, leading to the physiological study of this complex, and as an intellectual means to permit a more accurate interpretation of what occurs normally in humans during complex sensory tasks and what underlies abnormal visual processing in humans who have suffered damage to the thalamus.
| Pistorio, Ashley L; Hendry, Stewart H; Wang, Xiaoqin (2006) A modified technique for high-resolution staining of myelin. J Neurosci Methods 153:135-46 |
